Application of refutas model to estimate erythrocyte viscosity in a dextran solution

Abstract

Whole blood viscosity has been considered as a significant clinical parameter in diagnosis and prevention of various cardiovascular diseases and a useful reference to monitor certain diseases. The blood viscosity can be influenced by several factors, such as red blood cell aggregation, hematocrit, and plasma viscosity. In many cardiovascular disease conditions, the concentration of plasma proteins (particularly fibrinogen) increases and this effect may elevate the aggregation level of red blood cells as well as plasma viscosity. This kind of phenomenon can also be observed in many in vitro studies that utilize high molecular weight dextrans (Dextran 70 and Dextran 500) to induce red blood cell aggregation. The red blood cells in such a dextran medium in general show a tendency of aggregation. Furthermore, with increasing dextran concentration, not only the aggregation level but also medium viscosity rises. In such case, it becomes difficult to determine individual quantitative effects of aggregation and plasma viscosity on blood viscosity, in particular on red blood cell viscosity. Information on the red blood cell viscosity is important in the microcirculation since a phase-separation phenomenon becomes apparent in microvessels, which leads to formation of a plasma layer near the vessel wall and a red blood cell rich region near the centerline. Thus, the viscosity in the core region (red blood cell viscosity) becomes much higher than the effective viscosity of blood. The Refutas model was first introduced to estimate the viscosity of oil mixture. This model can be used to predict the viscosity of a fluid mixture by measuring viscosities of individual fluid components. Alternatively, this model can be used to estimate the viscosity of an unknown component from the viscosity of its mixture. In this study, we attempted to use the Refutas model in estimating the viscosity of packed red blood cells by measuring blood and medium viscosities. Thus, the main purpose of the present study was to examine possibility of applying Refutas model to quantify the sole effect of red blood cell aggregation on red blood cell viscosity.